Process for drying substances in the condition of sludge and for evaporating solutions



J1me 1938- r H. WENDEBORN PROCESS FOR DRYING SUBSTANCES IN THE CONDITION OF SLUDGE AND FOR EVAPORATING SOLUTIONS Filed July 24, 1936 2 Sheets-Sheet l Invenior': HE'JmuLZ u endeb 0112 A ttarn eg Patented June 7, 1938 PROCESS FOR. DRYING IN.

THE CONDITION OF SLUDGE AND FOR- EVAPORATING SOLUTIONS Hehnut Wendeborn,

l rankfort-on-the-Main,

Germany, assignor to American Lurgi Corporation, New York, N. York Y., a corporation of New Application July 24,1936, Serial No. 92,300 In Germany July 30, 1935 7 Claims.

This invention relates to a process for drying substances in the condition of sludge and for evaporating solutions.

In the treatment of fuel sludges, ore slimes,-

clay slurries, raw cement slurries, and the like, such as are obtained, for example in the wet preparation of these materials, it is necessary to remove the water if the materials are to be put through a further dry treatment or to be transported in a dried or pre-dried condition. The water content of said sludges often amounts to as much as 80%, and it will be evident that extensive plants and a considerable expenditure of heat are needed for its removal.

obviates these drawbacks, that is to say, in which the drying of the material is performed with very much less expense. It has been ascertained in accordance with the present invention that such 0 thin sludges as those already mentioned can be dried by means of a gaseous drying agent, with a considerable saving of heat, when they are arranged on a permeable fixed or progressively moving support,- by disposing the sludge on, or

mixing it with a granular carrier of the same, or similar material character as the finished product in view,'or of such character as to improve, or notimpair, the suitability of the dried product for use, the relative proportions being 30 so chosen that a non-fluid mass, which is suillciently permeable to gases is applied to the permeable support in a comparatively shallow layer,-

for example, cm. in depth.

The process is carried out by mixing the sludgewhich may contain for example, from 50 to 80% of water-with suificient quantities of a fine-grained carrier material toreducethe content of water to; about 20% or less, that is to say, a mass is obtained that is no longer fluid and 40 can be applied, in a condition permeable to gases, on the support in the drying apparatus. Instead of mixing the material to be dried and the carrier material before their transfer to the drying apparatus, the granular carrier may first be disposed on the permeable support, and the material to be dried is then spread over the surface of the carrier in such amount that the mass can be dried by passing a gaseous drying agent through 'it.' During or after the spreading of the layer of sludge on the carrier the drying mass formed can be influenced, by means of a shaker, turning device or in some other way, so as to increase the permeability thereof to the drying agent still further.

All solid substances which do not undesirably The present invention provides a process which modify the character of the material-and primariiy therefore substances of the same or similar nature as said material-are adapted for use as carrier. They should be loose substances of small grain size and preferably displaying a large superflcial area. In many cases it is of particular advantage to employ return material-that is to say .to divert a'portion of the dried product from a previous batch-as carrier material for thesludge'. a

In other cases it may be advisable to use different' carrier materials but of the same nature, for example when the drying is to be followed by --further treatment, in which case the product'of this treatment is used as a carrier for thesludge, using for example chaniotte for clay slurries, coke for fuel sludges and ore agglomerates for me sludges.

However, other substances may also be used as carriers insofar as they are necessary for or do not interfere with .the final treatment, such as for example certain metallurgical additions to the ore or the like, or coke, coal or the like, if the material to be dried is to be subjected to a sintering or reduction process. The carrier material must obviously, if it is not already in a fine-grained condition, be comminuted to the requisite grain size. Preferably the already finegrained portion of the product of the further treatment of material dried in accordance with the invention, will be used exclusively or mainly as a carrier material.

The grain sizes of the fine-grained carrier material are determined in each individual case according to the conditions obtaining thereinj Thus, for example, grain sizes below 3-20 mm. may be employed when raw cement flour in the form of sludge or ore sludge is first to be dried in accordance with the invention, and then sub- Jected to sintering or roasting upon blast grates. In any case the most suitable granular size can be simply and conveniently ascertained by a few tests. Moreover, it is obviously not necessary that the carrier material should possess a uniform grain-size, for it can frequently be used with success provided the grain-size does not exceed a certain upper limit, although being of all other possible sizes below that limit. 1

The evaporative eflect is the greater-the greater the suri'ace'presented by the charge material. By spreading the sludge over carrier material, a large superficial area is presented by the'former and is accessible, at all points, to the penetrat-' ing gases.

passing ordinary air-for example at 20"" C.

In this manner, a mixture of sludge and carrier material can be dried by merely.

55 The. original carrier material or a portion of the.

' the rapid and continuous removal o'f'the'water through the mass, the air issuing saturated with water vapour and quicklyjdrying the charge.

Even a slight increase in the air temperature considerably reduces the amount of air needed.

Thus, for example, the amounts of dry air required for the absorption of 1 kg. of water vapour at diflerent temperatures are:

; Q In the case of airof normal humidity,.i. e. undried air as is present in the atmosphere, the

amounts will-be correspondingly larger depending on said humidity. As is known, the rate of evaporation of water depends, not only on the temperature, but also on thepartial pressure-of the water vapour and the effective superficial areaavailable. .If,iby

' vapour. this partial pressure be maintained at a lower level than correspondsito the' conditions of equilibrium for a given temperature, evapora-' tion necessarily continues until the whole of .the water' presentin the origination material has This is noticeable in a highly favourable manner when the airis drawn through in excess. 1 1m general, the water vapour already passes oil from the charge in these circumstances, at temperaturesbetween 50 and 60 (2.,

' with a velocity attainable other conditionsa Two 'or more carrier materials of different nature can also be usedat the same time. Thus, for example a fine-grained? carrier material which has not been derivedfrom the dried material is first mixed with the'corresponding quantity of the sludge under-treatment, this mixture being dried. This dried material is then screened and.

a portion, for-example of coarser, liner. or medium' grain ,or the like, is separated as finished material, whilst the finer grain serves alone or.

with certain'quantities of the original carrier material as a carrier-for fresh quantities of the same sludge whichisto be dried. In this con-- nection the yield of 'fine-grained material can be increased by subjecting the dried-material to friction or-other gentle comm'inution, for example by treating. it'in arotating drum or on an oscillating screen, saidgentle comminution being allowed to proceed to such an extent that the dried material can be separated again wholly 'or' for the most part from theoriginal carrier material.

dried'material ora mixture of. bothsubstances with or without addition of other line'- grained substanees'gcan then be used. as carrier material :for fresh" quantities. of the material under treatment. 7 1

Theproces's onflin two oi,

more stages. In such eventitwodrying apps--v o e-d ed, as the dryin "gratqand w n; to the second ap.-

am or; harm gm; suitm the gunm are flnishinsipparltus 1m flbead'vantageously mumsier the firstapparatus. the process Mom i s manner.

only at 100 C; under 1 rial remaining for example, V. .screen-thatiaallwithagrain ratus, for example. in series. The sludge which, according to'the: invention, has al'-,- readyjbeen spread ,over the carrier is 'A'nother possible'method since the heat content of the exhaust gases from one drying stage is also utilized. It is also feasible to employ gases of different origin, for 'example exhaust gas and air in conjunction.

. Again, fresh quantities of thelthin' sludge under treatment canbe added in the second drying V apparatus to the already pre-dried material,

' thereby again raising its water content to about 20% before subjecting it to further drying.

'Ihe single-stage process and the two-stage process can also be combined to a certain extent *by passing, to the finishing dryer, only 'a certain portion and not the whole of the pre-dried mixture from the first dryer, and on occasion mixing the remainder of the latter withreturnmaterial from the finishing dryer, or other carrier material, the mixture being again passed, tov gether with fresh sludge, through the pre-dryer. In this manner, particularly large quantities of sludge, can be dried with a given amount of returnimaterial.

n desired,the-driedproduct obtained from the directly on the'grate on which they have been sludge may be further treated in the drying ape paratus itself. For example, ores can be sintered,

of the requisite quantities of fuel if desired. In

this-case the fuel needed for sintering can. be mixed with the sludge material before drying the I latter, the fluidity of which thereby already becomes somewhat reduced, so I that smaller amounts of other carrier substances are needed for the drying process, whilst, on the other hand,

after drying the fuel is already uniformly dis- :tributed in the product, so that uniformity in the disengagement of'heat is attained in the intering process. Alternatively, the product can,'of course, be

further treated in a specially designed apparatus directly, after thedrying is completed, for example onblast grates, in shaft furnaces or the like. v In addition to the treatment of sludge material, the process of the present invention isalso applicable to the evaporation of dilute or conoentrated solutions, such for example, as theliquors from. the potash industry, which are.

worked up to solid salts or the like. In this case,v

the carrier material employed consists, for example,- of saline crystals of a definite grain size.

say between 2 and 5 mm. These crystals are impregnated with Just a suiiicientamount of s'olution to leave the mixture permeable to gases.

The mixture is charged onto the blast grate and dried by a suction draught of hot gases. The

dried product is then screened'with or without careful comminution, the several stages of granu- 1ation being soar-ranged that, so far as is prac-.

ticable. a quantity of salt of the desired'grain size corresponding exactly to the evaporated so lutionis separated from the. bulk. The matemm.-is again treated with solution and returned. to the dryer. In this manner, there is mainservesfas ai-carrierffor fresh quantities ofrthe pica-mine out the solution under treatment.

on the coal size exceeding 2 25 I dried by the known blast'process, with addition e evaporation consists in first spreading over the grate a layer, about 10 to 20 cms. thick, of they previously crystallized salt-so as to be as permeable to gas as possible-and then moistening it (for example by spraying) with the concentrated solution to be evaporated, air, or other suitable gaseous drying agent, being passed through the charge at the same time.

In order more clearly to understand the invention, reference is made to the accompanying drawings, which illustrate diagrammatically and by way of example, apparatus suitable for carrying same into practical effect and in which:

Fig. 1 is a general flow-sheet; and

Fig. 2 shows a plant which is particularly suitable for drying ore sludges, raw cement slurries or the like, with subsequent sintering of the dried material.

Referring to Fig. 1, the fine-grained carrier substance is contained in the hopper I, and the solutionor in otherc'ases the sludge to be dried-in the vessel 2. The feeding device supplies said carrier substance from the hopper l to the mixer 3, into which the sludge or saline solution from the vessel 2 is supplied, at the same time, by means of nozzles. 4. The mixture of carrier substance and sludge (or saline solution) from the mixer is distributed over the actual drying grate 6 by way of the feed hopper 5, so as to form a layer-for example about 20 mms. deep-on the grate 8. which travels in the direction of the arrow, the mixture being dried by a suction draught of exhaust gases admitted by way of the hood 1, or else by means of air. The

drawing represents the drying arrangement,

partly with exhaust gases and partly with air.

The waste gases are supplied through'line i2 and hood I over the grate. whilstthe air passes mainly through that portionof the charge onv the grate which is not covered by hood- 1. The moist vapours .are exhausted from the wind chest B by means of a fan 9 and forced into a chimney vessel B contains fuel of a grain size below 2-3 mm. Said raw cement slurry and fuel flow in definite proportions into the mixer II. The vessel i5 contains return material having a grain size. for example from 0-4 mm., said return material being discharged into the knife conveyor l5. and being treated with a definite quantity of the mixture of slurry and fuel from vessel H by means of the slurry distributor IT. The resulting fairly moist mixture of slurry and return material together with fuel then passes into the hopper l8 of-the drying grate l9, which is of the travelling type, and is applied-over said grate to a depth of, for example 20 cms. b'eing carried along by the grate in the direction of the arrow.

The charge is then dried by drawing air or emu-- ent gases from the sintering process therethrough. The moist vapours resulting from said drying are drawn off from the wind-chest of the drying grate through line 2! by means of the blower 20. Fig. 2 indicates that the drying can also be carried out in a combined manner, 1. e. partly using eflluent gases and partly using air. in which connection the heating of the dried material by the sensible seat of the effluent gases can advantageously be utilized for preheating the dry air. The thus dried mixture leaves the travelling grate l0 and passes by means of the hopper 23 into a second knife conveyor 24, in which it receives a fresh addition of a mixture of slurry and fuel from vessel H by means of the slurry distributor 25, so that a fresh fairly -moist mixture is produced, which is introduced into the charging hopper 26 of the actual blast grate 21. The resulting mixture is ignited and sintered in known manner by drawing air there through. The efiiuent gases are drawn off by means of one or two blowers 28 and 29, and if desired, are passedby means of the hood 30 to the drying grate i9 as described in the foregoing. Blower 29 draws off the warm moist gases at a temperature of about 50-60 C. which first escape during the sintering, whilst blower 28 merely draws off the hotter dry waste gases.

However, it is also possible to draw off the entire quantity of gas by means of a blower under hood 30 at a temperature of about 100 C. for drying purposes. After a preliminary comminution the sintered material falls on to a screening device 3|, being thereupon separated by screening in known manner into coarser (clinker) and finer (return material). The return material produced at 32 is returned to the charge bunker I5 for return material from whence it recommences its cycle. The travelling grate may be replaced by other devices for pre-drying the mix ture, and a shaft furnace, for example, may be used as the combustion furnace. It should also be noted that, although it is of advantage to mix the fuel with the sludge, the fuel may however, also be mixed with the return material or finally added to the ready-prepared mixture.

Example for raw cement slurrz'es with 60% of water The production of 1 kg. of cement clinker from raw cement slurry with 60% of water requires about 3.8 kg. of said slurry, whilst, in the case of a circulation of return material, about 4.5 kg. of such material will suflice for 3.8 kg. of slurry.

The mixture treated on the grate is may consist, for example, of:

Parts Return material 4. 5

Slurry 1.

Coke breeze 0.14

and then contains about 17.4% of water. This is dried on the grate i9 by means of hot waste gases, or by drawing a current of air through the charge, 710 cal. being needed to drive off the contained water.

The dried material consists of:

Return material 4.5

- Dry slurry material 0.75

Coke breeze 0.14 In all 5.39

To this is added 1.9 kg. of raw cement slurry and 0.14 kg. of fuel. This mixture contains about 15.3% of water and is burned, in this condition, on the sintering apparatus 2.! in known manner. During the sintering about I10 cal. must be applied to evaporate the water, and for the production of 1 kg. of cement, about 500 cal. or 1210 Parts cal. in all. In so doing, the combustion of altov gether 0.28 kg. of coke furnishes about 1850 cal.

and the exothermic efl'ect of the formation of clinker, about 150 cal., a total of 2000 cal. The difference between 2000 cal. and-1210 cal., viz. 790 cal. passes oil? in the waste gases and is quite s'uiflcient to cover small heat losses and for drying the mixture on the grate l9which requires 710 cal.so that this process enables cement to be burned with practically the theoretical consumption of heat. As already mentioned, ,it is even possible to utilize the heat contained in air at 20 C. for evaporating the water content of the mixture on the drying grate l9, so that the amount of heat from the added fuel may be less than is theoretically required for carrying out the process. On the other hand, the utilization of the outside air for the purpose of evaporation entails the expenditure of power for driving the blower.

The amount of circulated return material for particularly wet slurry may also be reduced .by

pre-drying the slurry, or a portion thereof as such, by means of waste gases from blast-roasting apparatus said gases being passed through the known calcining apparatus and pre-drying urally impossible'to prevent the formation of' the employment of return material then enabling sludgy originating materials to be also economically treated in the shaft furnace, which was not heretofore directly feasible. Other cement furnaces, such as rotary-tube furnaces or ring furnaces, are also suitable for the final treatment.

The advantages of the process of the present invention consist in the possibility of burning any raw cement slurry, that contains less than 50% of water with practically the same expenditure of heat that is needed for burning raw cement powder produced by dry grinding. It is solely owing to this that the advantages of, the wet preparation of cement raw materials become fully apparent. In the, case of raw cement'slurries withmore than 50% ofwater -such as 50-80%- -the way is'thus open for carrying out p the calcining process with a minimum expendb ture of fuel bordering close on the theoretical limit." In known processes, slurry is spread over heat transmitters of a different nature-such as iron rings.and dried. After drying, the dried material must be separated from the carriers by applying movement to the latter, it being then natdust.

In the process of the present invention, on the contrary! (1) No foreign bodies are employed for the heat transmission, and therefore there is no'need for separating the carriers and dried material;

. (2) The return material serves primarily to distribute the slurry over a large surface and ren-Q dering it permeable to gases, and does not serve as a direct transmitter of heat; 1 I

(3) The drying of the widely distributed slurry ,y iseflec'ted by a steady-flow'of air or warm gases throughthematerial, ahigh rate of evaporation resulting from the rapid removal of the water vapour.

I claim: I V

1. The process of drying liquid water-bearing substances which comprises in combination 'mixing said substances with a granular carrier having no adverse efiect on the substances to be dried in such relative proportions that a no longer fluid mass but one adequately permeable to gases is obtained, charging the said mixture as a comparatively shallow layer on to a support suillciently permeable to gases, drawing gases through said layer to dry said mixture,'andsubsequently separating said dried substances from the said granular carrier. j

2. The process 01 drying liquid water-bearing substances which comprises in combination charging a granular carrier having no adverse efiect on the substance to bedried on to a support permeable to gases as a layer-cf suitable depth,'applying a liquid substance to be dried to the surface of. said carrier in such amount that a no longer fluid mass but a mixture permeable to gases is obtained, passing a gaseous drying medium through said mixture to dry the same, and subsequently separating said dried substance from said granular carrier.

3. The process of drying liquid water-bearing substances which comprises in combination charging a granular carrier constituted of a portion of the dried product on to asupport permeable to gases as a layer of suitable depth, applying a liquid substance to be dried to the surface of said carrier layer in such amount that a no longer fluid mass but a mixture permeable to gases is obtained, passing a gaseous dryingmedium through said mixture to drythe same, and

subsequently separating" said dried substance from said granular carrier.

4. The process of drying liquid water-bearin substances which comprises in combination mixing said substances witha granular carrier having no adverse effect on-the substances to be dried in such relative proportions that a no longer fluid .mass but one permeable to gases is obtained, charging the resulting mixture as a relatively shallow layer on to a support sufliciently vpermeable to gases, drawing gases through said layer for at least partially drying the said mixture, separating said-dried substances from said granular'carrier, mixing the at least partially dried substances with additional amounts of liquid raw materials, placing the second mixture thus obtained upon a-second support permeable to gases, and subsequently subjecting said second 1 mixture to further heating at a temperatur exceeding the drying temperature. 5. The process of producing cement from rawv materials in the form of sludge. which comprises admixing said sludge with a granular carrier substance having substantially no detrimental eifect on the properties of the finished product 6. The process of producing cement from raw efiect on the properties of the finished product in such relative proportions that a no longer fluid mass but one permeable to gases is obtained, charging the resulting mixture as a relatively shallow layer ,on to a traveling grate, drawing gases through said layer to at least partially dry said'mixture, separating said dried substances from said granular carrier, mixing the at least partially dried substances with additional amounts of fresh sludge, placing the second mixture thus obtained upon a second traveling grate,- and subsequently calcining said second mixture. I a

"l. Theprocess of producing cement from raw -materials in the form of sludge which comprises admixing said sludge with a granular carrier substance formed in the calcination of cement in such relative proportion that a no longer fluid mass but one permeable to gases is obtained, charging the resulting mixture as a reladrawing gases through said layer to at least partially dry said mixture, separating said dried substances from said granular carrier, mixing the at least partially dried substances with additional amounts of fresh sludge, placing the second mixture thus obtained on a second traveling grate, calcining said second mixture, and re- HELMUT WENDEBQRN.

tively' shallow layer on to a travelling grate,

turning a portion of said calcined material for to 15 'be admixed with fresh sludge to be treated. 

